
let p = new Promise((resolve,reject)=>{
    setTimeout(() => {
      resolve('first')
    }, 1000);
});
p.then(res=>{
  console.log(res);
  return Promise.resolve('second')
}).then(res=>{
  console.log(res);
  return Promise.resolve('third')
}).then(res=>{
  console.log(res);
})
// first
// second
// third